Most vehicular tires have a rubber tread of a lug and groove configuration. Many tires are of a co-extruded cap/base construction, wherein the tread cap is an outer rubber layer which contains the lug and groove configuration.
The outer lug surfaces of the tread are normally intended to be the running surface of the tire to promote ground-contacting traction for the tread.
The grooves of the tread located between the tread lugs are normally intended to promote ground engaging grip for the tread.
It is appreciated that, for some tire treads, the tread lugs are in a form of individual lugs and/or of circumferential ribs. For the purpose of this invention, tread lugs and ribs are referred to herein as tread lugs, with intervening grooves, unless otherwise indicated.
When such lug and grooved configured tire treads are driven through water over roads, particularly hard surfaced road surfaces, which may contain standing or running water, it is important for the tread grooves to quickly expel the water to promote ground engaging tire tread traction on the road surface.
When such lug and groove configured tire treads are driven on or through soft wet substrates such as, for example when driving through mud, portions of the substrate (e.g. mud) can become lodged within the tread grooves in a sense of adhering to the surface of the tread grooves and which may at least partially clog at least a portion of the grooves to thereby adversely affect the ground engaging ability of the tread.
It is, therefore, desired to reduce adhesion, or adherence, of water and of wet and dry substrates to the tread groove surfaces, such as, for example, mud and dirt over which the tire tread travels, including mud which has dried within the tread grooves, and/or water itself without a significant substrate content, in a sense of providing increased lubricity to reduce the coefficient of friction of the groove surfaces insofar as water and various wet and dry substrates within the grooves is concerned and increased hydrophobicity to resist or retard water adhering to the tread groove surfaces and/or clogging of the tread grooves with water-containing substrates such as for example, mud (e.g. water-containing dirt) which may otherwise tend to adhere to the tread groove surfaces.
For this invention, such repellent property for the groove surfaces is provided by a thin polymer layer (e.g. elastomer layer) which constitutes at least a portion of the groove surface and which contains, or is comprised of, at least one repellent material within its composition and on its surface.
The presence of a hydrophobic property of the surface of the polymer layer (e.g. integral elastomer layer, namely an elastomer integral with the rubber of the tread groove over which it lies) on the tread groove surface is for the groove surface to tend to repel water and/or water-containing substrates, particularly mud, or water-containing dirt, to thereby reduce adhesion of water and/or at least a portion of the water-containing substrate to the groove surface and retard clogging of the tread grooves.
The presence of a lubricity property of the surface of the polymer layer on the surface of the tread groove (e.g. elastomer layer) is for the groove surface to promote a reduced (e.g. lower) dry and particularly wet coefficients of friction to thereby retard, or prevent, adhesion of water and/or wet and dry substrates such as dirt or dried mud to the groove surface to reduce clogging of the tread grooves and/or to improve the ground-gripping ability of the tread.
For this invention, the higher hydrophobicity and lubricity properties for the groove surfaces is promoted by providing the aforesaid polymer layer (e.g. integral elastomer layer) with a dispersion of at least one of hydrophobic and lubricant materials. Therefore, at least a portion of the groove surfaces contains at least one of, or a combination of, hydrophobic and lubricant materials provided by said polymer (e.g. elastomer) layer.
In the description of this invention, the terms “rubber” and “elastomer” if used herein, may be used interchangeably, unless otherwise prescribed. The terms “rubber composition”, “compounded rubber” and “rubber compound”, if used herein, are used interchangeably to refer to “rubber which has been blended or mixed with various ingredients and materials” and such terms are well known to those having skill in the rubber mixing or rubber compounding art.
In the description of this invention, the term “phr” refers to parts of a respective material per 100 parts by weight of rubber, or elastomer. The terms “rubber” and “elastomer” may be used interchangeably unless otherwise indicated. The terms “cure” and “vulcanize” may be used interchangeably unless otherwise indicated.
For this description, the term “butyl rubber” relates to a copolymer of isobutylene and conjugated diene (e.g. isobutylene and a minor amount of isoprene) and is intended to include halobutyl rubber (halogenated butyl rubber) such as for example, bromobutyl and chlorobutyl rubber, unless otherwise indicated.